Common electrical receptacles are provided with a number of open apertures into which a male electrical plug can be inserted. When the plug is not in place, these open apertures provide a path through which foreign objects and dirt may enter the electrical receptacle. Not only do foreign objects and dirt pose a problem with respect to the performance of the receptacle but the open receptacle apertures periodically cause injury to infants and small children who insert conductive objects therein. A need exists to prevent the insertion of foreign objects and dirt into an electrical receptacle aperture when the receptacle is not in use. The mechanism used to achieve this result needs to be economically feasible and convenient in order to be practical.
One method frequently employed to shield unused electrical receptacles is to insert a non-conductive dummy male plug into the receptacle to cover the apertures. Such devices are effective for young infants, however, more dexterous children in the 11/2 to 3 year old age group can easily remove the dummy plugs to expose the open receptacle apertures.
A number of prior art electrical receptacles have been developed having internal aperture shields. An example of a device intended to exclude foreign objects yet allow conventional two or three prong male plugs is shown in U.S. Pat. No. 4,379,607 (Bowden). Electrical receptacles have bee provided with internal aperture shields which prevent the insertion of objects into the receptacle with the exception of plugs having a ground prong as shown in U.S. Pat. Nos. 2,579,538 (Bierce), 3,736,547 (Koenig) and 4,168,104 (Buschow). These devices restrict entry of foreign objects into the receptacle, however, standard two prong plugs may not be inserted.
A great number of electrical appliances sold today do not utilize a three prong plug. It is therefore desirable to have an electrical receptacle provided with internal aperture shields which will accept both grounded as well as ungrounded male plugs. All newer two prong appliances sold in the United States are polarized so that the plug may be only inserted in a specified orientation relative to the receptacle. Polarization is achieved by making the height of one of the two blades significantly greater than the other and sizing the corresponding apertures in the receptacle so that the plug can only be inserted the receptacle in a specific manner. It is desirable to have an electrical receptacle which will keep out foreign objects but also selectively exclude non-polarized two prong plugs which are found on obsolete and unsafe electrical appliances.
As pointed out in Barkus U.S. Pat. No. 4,544,219 prior art receptacles such as that shown in Bowden U.S. Pat. No. 4,379,607 are compatable only with 15 amp plugs and cannot offer protection in applications such as hospitals, child care centers, institutional or commercial buildings where the more common receptacles the 20 amp type. Barkus addressed this problem using a two shutter mechanism, designed to operate when two objects of sufficient rigidity are inserted in the slots. Barkus like Bowden, Jr., have the same inherent problem, all that is required to operate the shutters are objects of sufficient rigidity such as hair pins, keys, nail files, toys or like objects. It was with this deficiency in mind that the present safety receptacle was developed. What was needed to meet the requirements of the National Electric Code was a new and novel receptacle that could determine if the attempted insertion of objects into the aperture openings are foreign objects or a legitimate NEMA plug component (National Electric Manufacturers Association). This invention solves that problem, operating like an intelligent lock, it measures the object inserted and if the key fits it opens. The key being a component or components of a plug that must meet NEMA dimensions. Working models have proved that the receptacle will recognize as little as 0.003 of an inch of variation from NEMA design standards. The invention can be utilized with plug components that are parallel, perpendicular, T-Slot, L-slot, 2 blade, 3 blade, blades of different dimensions or any combination that would be required. The receptacle illustrated in the drawings is of a NEMA 5-20 configuration, however, the receptacle could be modified so the slide is capable of travel in either direction as would be required in a NEMA 6-20. Also, the number of shiftable locks could be increased to monitor any number of plug blade dimensions.
Accordingly, it is an object of the present invention to provide an electrical receptacle having an internal aperture shield preventing the entry of dirt and foreign objects into the receptacle openings. It is a further object of the invention to allow the aperture shield to automatically open upon the insertion of a grounded three prong plug or a polarized two prong plug and to selectively exclude non-polarized two prong plugs and foreign objects.
Another object of the present invention is to enable a receptacle to accept a twenty-amp plug having the conductive blades oriented at right angles to one another. A advantage of the present invention is that the desired performance characteristics can be obtained quite economically.
These and other objects, features and advantages of the invention will be apparent upon further review of the description of the preferred embodiment.